This invention relates to an improved electromechanical actuator for driving or controlling a plurality of regulating mechanisms such as a needle positioning mechanism and/or a work feed regulating mechanism, each operatively influencing the formation of successive stitches.
In the prior sewing machine, linear or oscillating actuators have been introduced which drive or control a plurality of regulating mechanisms such us a needle positioning mechanism or a feed regulating mechanism for use in the formation of stitches. As a consequence, the actuators must be arranged individually within a casing of a sewing machine. The space within the casing is, however, limited so that it becomes extremely troublesome when actuators are mounted together with other components in said casing.
In order to overcome the shortcomings found in the prior art, an electrical motor arrangement is disclosed in U.S. Pat. No. 4,143,606 issued Mar. 13, 1979 and Pat. No. 4,092,569 issued May 30, 1978. That is to say, the motor includes a pair of permanent magnets arranged in spaced opposite polar relationship to define magnetic field there-between, and three cylindrical armatures disposed within said field, and output shafts each connected integral with said armatures so that a needle positioning mechanism and other mechanisms will be driven through said output shafts.
However, in the motor disclosed, the magnet is flat-shaped while the armatures have a cylindrical configuration. The air gap between the magnet and the armature differs at each circumferential point of the armature. This results in the average air gap being relatively wide so that a big magnet is required to compensate for large leakage of flux. Eventually the disclosed motor will unavoidably become big in size.